1. A materialized view is defined as a table which is actually physically stored on disk, but is really just a view of other database tables. In PostgreSQL, like many database systems, when data is retrieved from a traditional view it is really executing the underlying query or queries that build that view.
2. A materialized view, or snapshot as they were previously known, is a table segment whose contents are periodically refreshed based on a query, either against a local or remote table. Using materialized views against remote tables is the simplest way to achieve replication of data between sites.
http://www.revsys.com/blog/2006/jan/03/when-to-use-a-materialized-view-in-postgresql/ (1.); https://oracle-base.com/articles/misc/materialized-views (2.)